The research outlined in this proposal is aimed at elucidating the mode of biosynthesis of a number of antibiotics. Compounds to be studied are pyrrolintrin, the hydroaromatic antibiotics dihydrophenylalanine, ketomycin and anticapsin, some benzoisochromane quinone antibiotics, the two boron-containing antibiotics aplasmomycin and boromycin, several macrocyclic lactones (chlorothricin, naphthomycin, ansatrienine) and, if possible, lysolipin and thiostreptone. Biological structure modification based on biosynthetic information is also envisioned with some of these compounds. The methods to be used include (a) feeding experiments with precursors labeled with radioactive isotopes, but also to a larger extent the use of 13C-and deuterium labeled compounds in conjunction with Fourier Transform NMR Spectroscopy, (b) isolation of enzymes carrying out some of these transformations and (c) synthesis and use of stereospecifically labeled substrates to probe the stereochemistry and mechanism of some of the biosynthetic reactions.